Du-Bro Threaded Couplers 4-40 Part No: 336. Designed for use with Du-Bro Kwik-Links and ball links. One end has no threads and can be soldered on and the other side has either 2-56 or 2MM threads. #336 4-40 Threaded Coupler is machined out of steel for maximum strength. Thread length is 5/8" (15.8 mm) long with 4-40 threads and an overall length of 1 1/2" (38 mm). Nickel plated for easy soldering.